1. Field of the Invention
This invention relates to an electrical connection between copper doped wire and copper doped aluminum bonding pads forming a part of a semiconductor circuit.
2. Brief Description of the Prior Art
It is often desirable to utilize doped metallization in semiconductor devices. A first doped aluminum metallization including the bonding pads are required to obtain certain desired metallurgical characteristics on semiconductor devices. When alloyed with a second metal, e.g., copper, significantly increased hardness and toughness of the aluminum metallization is achieved. These characteristics are fundamental to an integrated circuits's ability to withstand the thermal stress, induced in the active circuitry of the device by the expansion and contraction of plastic encapsulant. The ability of a plastic encapsulated semiconductor device to withstand stress induced during temperature cycling between -66 degrees C. and 150 degrees C. is a requirement outlined in mil-standards and by most major commercial users. As the bonding pad becomes harder, the standard gold wire (a third metal) becomes less apt to properly bond thereto as compared to the undoped bonding pad wherein the gold is relatively soft compared with the doped bonding pad. It is known that wires generally should be harder than the bonding pad material. The wire of choice presently used in semiconductor applications is a gold wire. Gold wire doped with a fourth metal, beryllium for use in semiconductor applications is discussed in an article entitled Metallurgical Behavior of Gold Wire In Thermal Compression Bonding, T. H. Ramsey, Solid State Technology, October 1973, pages 43 to 47, which is incorporated herein by reference.
However, a problem exists with the current technology of thermosonic ball bonding of standard beryllium doped gold wire to copper doped aluminum metallization in the form of bonding pads due to the increased hardness and toughness in that standard gold wire of the type described hereinabove is of insufficient hardness to cause the level of plastic flow of the integrated circuit metallization as was achieved with standard aluminum integrated circuit metallization. It is therefore necessary to provide wire for bonding to copper doped aluminum pads which is of sufficient hardness to overcome the problems noted hereinabove and provide a reliable bond to the pad.